A variety of techniques are used to stack integrated circuits into a module. Some require that the circuits be encapsulated in special packages, while others use circuits in conventional packages. Both leaded and BGA type packaged integrated circuits (ICs) have been stacked. Although BGA packaging has become widely adopted, leaded packages are still employed in large volumes in low cost applications such as, for example, flash memory, which, when packaged, is typically found in thin small outline packages otherwise known as TSOPs.
Other technologies have been devised to stack bare die or flip-chip configured integrated circuits. In a typical example, flex circuitry upon which such integrated circuits have been affixed has been employed to supplant the role of encapsulating packaging. In some strategies, flex circuitry bearing bare or flip-chip die is folded over itself to yield a multi-level module in which the constituent die are disposed vertically one above the other with module contacts being provided along one or more surfaces of the flex circuitry. In other strategies, such as purportedly disclosed in U.S. Pat. No. 6,388,333 to Taniguchi, et al., a substrate bears an integrated circuit die that is encapsulated by a seal material having a height less than protruding electrodes connected to pads on the redistribution substrate which are connected to the die. Other previous systems have purportedly disposed flip-chip devices with active face down on substrates that are connected one to another through conductive members as described in U.S. Pat. No, 6,781,241 to Nishimura et al.
Thermocompression bonding and thermosonic bonding are processes used for single-side bonding, for example, in the manufacture of LCD displays. Previous thermocompression or thermosonic bonding systems are typically used to affix die only to one side of a substrate, such as in certain flip chip configurations. Accordingly, what is needed is a system and method for bonding die on opposite sides of a substrate using thermocompression or thermosonic bonding.
Most previous systems that employ unpackaged die have provided complex structures with attendant scalability and construction technique complexities. Consequently, what is needed is a system and method for stacks and stacking die that is readily adaptable to scalability, while using well understood materials with facility for known good die management.